CBQE-0: some comments in restart_cbrecover_multiple_failover_swapout_reb_routine

Change-Id: I81d330656a4ca56496b0c69e9937be3c2eed2330
Reviewed-on: http://review.couchbase.org/38407
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>